\begin{matrix} 的对齐问题

Question

我正在尝试生成这个等式：

使用以下内容：

\begin{equation}
    d(T,b)=\left\{\begin{matrix}
    0 & \mathrm{if branch has been covered,}\\ 
    v(d_{min}(t\in T, b)) & \mathrm{if the predicate has been executed at least twice,}\\ 
    1 & \mathrm{otherwise.}
    \end{matrix}\right.
\end{equation}

但我得到了这个：

首先，我该如何修复对齐方式，使其与上面代码片段中的对齐方式完全相同？另外，我该如何修复右侧的文本？包括第二个值中的换行符？

Answer 1

cases使用专用环境或其dcases*变体（由 定义）来执行此操作要简单得多mathtools：

\documentclass{article}
\usepackage{mathtools}

\begin{document}

\begin{equation}
d(T,b)=\begin{dcases*}
0 & if branch has been covered, \\
v(d_{\min}(t\in T, b)) & \parbox[t]{15em}{if the predicate has been executed at least twice,}\\
1 & otherwise. \\
\end{dcases*}
\end{equation}

\end{document} 

Answer 2

为了不猜测宽度，您可以使用tabular：

\documentclass{article}
\usepackage{amsmath}

\newcommand{\btext}[1]{%
  \begingroup\renewcommand{\arraystretch}{1}%
  \begin{tabular}[t]{@{}l@{}}#1\end{tabular}
  \endgroup
}

\begin{document}

\begin{equation}
d(T,b)=
\begin{cases}
  0                      & \text{if branch has been covered,}\\[0.5ex]
  v(d_{\min}(t\in T, b)) & \btext{if the predicate has been \\
                             executed at least twice,}\\[3ex]
  1 & \text{otherwise.}
\end{cases}
\end{equation}

\end{document}

的（本地）重置\arraystretch是必要的，因为cases会改变它。仍然需要一些猜测，以便分离行。

Answer 3

这只是array和的组合matrix……但对于环境来说，cases这是公正且正确的解决方案。

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools,amssymb}
 
\begin{document}
\begin{equation*}
   d(T,b)=\left\{\begin{array}{lll}
      0 \\ 
      v(d_{\min}(t\in T, b)) \\
      1
    \end{array}\right.
    \begin{matrix*}[l]
\text{if branch has been covered,}  & \\
\text{if the predicate has been executed at least twice,}& \\
\text{otherwise.}
\end{matrix*}
\end{equation*}

\end{document}

Answer 4

您可以使用这个包来做这件事cases。

\documentclass{article}
\usepackage{cases}

\begin{document}
\begin{numcases}{d(T,b)=}
  0                             & if branch has been covered, \nonumber \\
  v(d_{\mathrm{min}}(t\in T,b)) & \parbox[t]{11em}{if the predicate has been executed at least twice,} \nonumber \\
  1                             & otherwise \nonumber
\end{numcases}
\end{document}